Molecular Mechanisms of Proteasome Inhibitor-Induced Peripheral Neuropathy

Introduction: Chemotherapy-induced peripheral neurotoxicity (CIPN) is a common side effect of numerous chemotherapy treatments for cancer. 20S proteasome inhibitors, such as bortezomib (BTZ) and carfilzomib (CFZ), have been approved for the treatment of multiple myeloma but cause CIPN of different severity, possibly dependent on different neurotoxic mechanisms. Indeed, only BTZ has been shown to exert a specific off-target binding to tubulin which may lead to microtubule stabilisation and axonal degeneration. BIPN has been replicated in a preclinical setting, while there is still no model of CFZ-induced neuropathy. We focused on developing a solid mouse model of CFZ-dependent CIPN in order to compare it to BTZ-induced neurotoxicity. We then analysed the differential impact of the two drugs on cytoskeleton and mitochondria in primary cultures of sensory neurons. Methods: We used behavioural, morphological, and morphometric measurements to characterize the induced neuropathy in vivo. Furthermore, we assessed the effect of both drugs on neuronal survival and growth, mitochondrial function and trafficking, and mitochondrial and cytoskeletal proteins expression in cultured mouse dorsal root ganglion neurons treated for 10 or 24 hours with 10nM BTZ and 60nM CFZ. Results: We found that BTZ induces more severe neuropathic symptoms and pain that correlate with loss of large and intraepidermal nerve fibres compared with the CFZ animal model. In vitro, both BTZ and CFZ similarly induce a significant decrease of mitochondrial function after 24 hours of treatment. However, mitochondrial trafficking analysis revealed a significant increase in stationary mitochondria only after BTZ treatment. Moreover, only BTZ exerts a direct effect on microtubules showing microtubule stabilization as early as 10 hours after treatment. Conclusions: Taken together, these results characterize a novel CFZ-induced neurotoxicity model and highlight the differences in neurotoxicity mechanisms between diverse proteasome inhibitors, paving the way for tailored therapeutic strategies. This work is supported by Fondazione Cariplo, Grant # 2019-1482.